News

2010

Technical Report Vol.4

Generating Highly Precise Motor Models based on FEA

The modeling technology built into JMAG can automatically generate a model
specifically for a circuit/control simulation from an FEA model. The most
profound aspect of these types of models is the high level of accuracy
they provide. There are a wide range of methods for modeling motors specific
to circuit/control simulations. The motor modeling technology built into
JMAG provides a motor model that satisfies the accuracy that is required
while maintaining the time the model is generated.

(a) Direct coupling model
This type of analysis can be more easily understood if it is considered
a coupled analysis that links FEA and the circuit/control simulation. In
other words, this method allows the FEA model to be used directly in the
circuit/control simulation to achieve a level of accuracy in the circuit/control
simulation that is equal to FEA. Valuable insight can be captured by confirming
distributions as results from a simulation, such as the magnetic flux density.
One of the disadvantages of this type of model is the time required for
calculation using the FEA model when there are a large number of elements
because the finite element method is performed sequentially.

(b) LdLq model
An LdLq model is generated to include the inductance of a motor from an
FEA model. This type of model is based on models that are composed of mathematical
equations. However, the inductance of a motor varies with magnetic saturation.
The LdLq models generated by JMAG take the magnetic saturation into account.
Even though this is a conventional type of model, the accuracy of the parameters
increases based on the analyses capabilities of JMAG.

(c) JMAG-RT model
A JMAG-RT model is a behavior model generated from an FEA model. The model
is based on the same principles as the LdLq model, but the JMAG-RT model
enhances the accuracy by not only accounting for the nonlinear characteristics
of the motor but also the effects of the spatial harmonics.
The models described in (b) and (c) based on the conventionally classic
type of model reduce the time required for a circuit/control simulation
when compared to the model described in (a) while enhancing the accuracy
of the parameters.

Why a Motor Model Based on FEA is Necessary

This technical report has described why a highly accurate motor model is
important, but why does this type of model need to be generated from a
JMAG model (FEA model)?
First is the accuracy. The magnetic field analysis based on the finite
element method JMAG provides is becoming indispensable in the motor design
process. The analysis technology built into JMAG accurately visualizes
the complex motor behavior required by motor designs. MBD cannot be realized
of course if the evaluation of motors in a circuit/control analysis is
not equally as accurate. This means that the accuracy of the model that
is generated directly corresponds to the accuracy of the motor model.
I would also like to touch on safety, even though it is not directly related
to the motor model itself. The control algorithm is tested using a prototype
under various drive conditions. Tests, such as the maximum rotation speed
as well as the robustness of the motor when operating abnormally, such
as short circuits, involve a certain degree of danger that increases the
costs that are incurred. MBD can reduce the danger and the cost that are
incurred via simulation even though a behavior of a motor operating abnormally
diverges largely from the steady state. The accuracy is also indispensable
to evaluate a motor operating abnormally. Therefore, a highly accurate
motor model is required to maintain a high level of safety.
The same motor model generated from an FEA model can be used for both the
motor design and circuit/control design. This type of model opens a dialog
between the motor designer and circuit/control designer through MBD, providing
a tool that can not only be used for analysis, but also a communication.
The motor design and circuit/control design required to develop products
are connected by the motor model generated by JMAG as well as JMAG itself.